Comparative uptake of rat and human serum low-density and high-density lipoproteins by rat aortic smooth muscle cells in culture.

Rat aortic smooth muscle cells in culture were exposed to rat and human serum (LDL) and high-density (HDL) lipoproteins labeled with 125-I. 125-I-lipid was taken up preferentially from all of the lipoproteins used. 125-I-protein uptake of both rat LDL and HDL was significantly higher than that of the corresponding human lipoproteins, and human LDL was preferred to human HDL. The uptake of delipidated high-density apolipoproteins of either rat or human origin was very low. About 3-4% of the interiorized rat LDL and HDL was catabolized during 48 hours of incubation. On electron microscopic autoradiography of cells incubated with rat 125-I-LDL, the concentration of label, representing mainly 125-I-protein, was associated with secondary lysosomes. These results suggest that, if the protein uptake represents particle uptake, the preferential uptake of human LDL compared with human HDL could account in part for the finding that LDL acts as a more potent feedback suppressor of 3-hydroxy-3-methylglutaryl CoA reductase than does HDL.